From November 2016 I am a post-doctoral researcher at the Observatory of Geneva (Department of Astronomy of the University of Geneva) dedicated to the search of extrasolar planets and the study of stellar magnetic activity.
Before that I was a PhD student at the Instituto de Astrofísica de Canarias (IAC) and the University of La Laguna (ULL). My PhD thesis deals with the search of low mass extrasolar planets using high resolution spectroscopy. It was also focused on the detection and characterization of radial velocity signals induced by stellar activity, which can be easily mistaken for planetary signals.
Up to now my work has resulted in seven first-author articles, thirteen articles as co-author and several talks and posters.
First author articles
–HADES RV Programme with HARPS-N at TNG. VII. Rotation and activity of M-Dwarfs from time-series high-resolution spectroscopy of chromospheric indicators (A&A Accepted)
We aim to investigate the presence of signatures of magnetic cycles and rotation on a sample of 71 early M-dwarfs from the HADES RV programme using high-resolution time-series spectroscopy of the Ca II H & K and Halpha chromospheric activity indicators, the radial velocity series, the parameters of the cross correlation function and the V-band photometry. We used mainly HARPS-N spectra, acquired over four years, and add HARPS spectra from the public ESO database and ASAS photometry light-curves as support data, extending the baseline of the observations of some stars up to 12 years. We provide log(R’hk) measurements for all the stars in the sample, cycle length measurements for 13 stars, rotation periods for 33 stars and we are able to measure the semi-amplitude of the radial velocity signal induced by rotation in 16 stars. We complement our work with previous results and confirm and refine the previously reported relationships between the mean level of chromospheric emission, measured by the log(R’hk), with the rotation period, and with the measured semi-amplitude of the activity induced radial velocity signal for early M-dwarfs. We searched for a possible relation between the measured rotation periods and the lengths of the magnetic cycle, finding a weak correlation between both quantities. Using previous v sin i measurements we estimated the inclinations of the star’s poles to the line of sight for all the stars in the sample, and estimate the range of masses of the planets GJ 3998 b and c (2.5 – 4.9 Mearth and 6.3 – 12.5 Mearth), GJ 625 b (2.82 Mearth), GJ 3942 b (7.1 – 10.0 Mearth) and GJ 15A b (3.1 – 3.3 Mearth), assuming their orbits are coplanar with the stellar rotation.
–The RoPES project with HARPS and HARPS-N. I. A system of super-Earths orbiting the moderately active K-dwarf HD 176986 (A&A Accepted)
We report the discovery of a system of two super-Earths orbiting the moderately active K-dwarf HD 176986. This work is part of the RoPES RV program of G- and K-type stars, which combines radial velocities (RVs) from the HARPS and HARPS-N spectrographs to search for short-period terrestrial planets. HD 176986 b and c are super-Earth planets with masses of 5.74 and 9.18 Earth masses, orbital periods of 6.49 and 16.82 days, and distances of 0.063 and 0.119 AU in orbits that are consistent with circular. The host star is a K2.5 dwarf, and despite its modest level of chromospheric activity (log(R’hk) = – 4.90 +- 0.04), it shows a complex activity pattern. Along with the discovery of the planets, we study the magnetic cycle and rotation of the star. HD 176986 proves to be suitable for testing the available RV analysis technique and further our understanding of stellar activity.
–HADES RV Programme with HARPS-N at TNG: V. A super-Earth on the inner edge of the habitable zone of the nearby M-dwarf GJ 625 (A&A 09-2017)
We report the discovery of a super-Earth orbiting at the inner edge of the habitable zone of the star GJ 625 based on the analysis of the radial-velocity (RV) time series from the HARPS-N spectrograph, consisting in 151 HARPS-N measurements taken over 3.5 yr. GJ 625 b is a planet with a minimum mass M sin i of 2.82 0.51 Mearth with an orbital period of 14.628 days at a distance of 0.078 AU of its parent star. The host star is the quiet M2 V star GJ 625, located at 6.5 pc from the Sun. We find the presence of a second radial velocity signal in the range 74-85 days that we relate to stellar rotation after analysing the time series of Ca II H&K and H alpha spectroscopic indicators, the variations of the FWHM of the CCF and and the APT2 photometric light curves. We find no evidence linking the short period radial velocity signal to any activity proxy.
–Characterization of the radial velocity signal induced by rotation in late-type dwarfs (MNRAS 05-2017)
We investigate the activity-induced signals related to rotation and magnetic cycles in late-type stars (FGKM) and analyse the Ca II H&K, the H α and the radial velocity time series of 55 stars using the spectra from the HARPS public data base and the light curves provided by the All Sky Automated Survey. We search for short-term and long-term periodic signals in the time series of activity indicators as well as in the photometric light curves. Radial velocity data sets are then analysed to determine the presence of activity-induced signals. We measure a radial velocity signal induced by rotational modulation of stellar surface features in 37 stars, from late-F-type to mid-M-type stars. We report an empirical relationship, with some degree of spectral type dependency, between the mean level of chromospheric emission measured by the logR’hk and the measured radial velocity semi-amplitude. We also report a relationship between the semi-amplitude of the chromospheric measured signal and the semi-amplitude of the radial velocity-induced signal, which strongly depends on the spectral type. We find that for a given strength of chromospheric activity (i.e. a given rotation period), M-type stars tend to induce larger rotation-related radial velocity signals than G- and K-type stars..
–A super-Earth orbiting the nearby M dwarf GJ 536 (A&A 01-2017)
We report the discovery of a super-Earth orbiting the star GJ 536 based on the analysis of the radial-velocity time series from the HARPS and HARPS-N spectrographs. GJ 536 b is a planet with a minimum mass Msini of 5.36 ± 0.69 M⊕; it has an orbital period of 8.7076 ± 0.0025 d at a distance of 0.066610(13) AU, and an orbit that is consistent with circular. The host star is the moderately quiet M1 V star GJ 536, located at 10 pc from the Sun. We find the presence of a second signal at 43 d that we relate to stellar rotation after analysing the time series of Ca II H&K and Hα spectroscopic indicators and photometric data from the ASAS archive. We find no evidence linking the short period signal to any activity proxy. We also tentatively derived a stellar magnetic cycle of less than 3 yr.
We investigate the photometric modulation induced by magnetic activity cycles and study the relationship between rotation period and activity cycle(s) in late-type (FGKM) stars. We analysed light curves, spanning up to nine years, of 125 nearby stars provided by the All Sky Automated Survey (ASAS). The sample is mainly composed of low-activity, main-sequence late-A to mid-M-type stars. We performed a search for short (days) and long-term (years) periodic variations in the photometry. We modelled the light curves with combinations of sinusoids to measure the properties of these periodic signals. To provide a better statistical interpretation of our results, we complement our new results with results from previous similar works. We have been able to measure long-term photometric cycles of 47 stars, out of which 39 have been derived with false alarm probabilities (FAP) of less than 0.1 per cent. Rotational modulation was also detected and rotational periods were measured in 36 stars. For 28 stars we have simultaneous measurements of activity cycles and rotational periods, 17 of which are M-type stars. We measured both photometric amplitudes and periods from sinusoidal fits. The measured cycle periods range from 2 to 14 yr with photometric amplitudes in the range of 5-20 mmag. We found that the distribution of cycle lengths for the different spectral types is similar, as the mean cycle is 9.5 yr for F-type stars, 6.7 yr for G-type stars, 8.5 yr for K-type stars, 6.0 yr for early M-type stars, and 7.1 yr for mid-M-type stars. On the other hand, the distribution of rotation periods is completely different, trending to longer periods for later type stars, from a mean rotation of 8.6 days for F-type stars to 85.4 days in mid-M-type stars. The amplitudes induced by magnetic cycles and rotation show a clear correlation. A trend of photometric amplitudes with rotation period is also outlined in the data. The amplitudes of the photometric variability induced by activity cycles of main-sequence GK stars are lower than those of early- and mid-M dwarfs for a given activity index. Using spectroscopic data, we also provide an update in the empirical relationship between the level of chromospheric activity as given by log10R ‘HK and the rotation periods.
–Rotation periods of late-type dwarf stars from time series high-resolution spectroscopy of chromospheric indicators (MNRAS 05-2015)
We determine rotation periods of a sample of 48 late F-type to mid-M dwarf stars using time series high-resolution spectroscopy of the Ca II H&K and H α chromospheric activity indicators. We find good agreement between the rotation periods obtained from each of these two indicators. An empirical relationship between the level of chromospheric emission measured by log R’hk and the spectroscopic rotation periods is reported. This relation is largely independent of the spectral type and the metallicity of the stars and can be used to make a reliable prediction of rotation periods for late K to mid-M dwarfs with low levels of activity. For some stars in the sample, the measured spectroscopic rotation periods coincide, or are very close, to the orbital periods of postulated planets. In such cases, further studies are needed to clarify whether the associated periodic radial velocity signals reveal the existence of planets or are due to magnetic activity.
Articles as co-author
–A system of tree transiting super-Earths in a cool dwarf star (MNRAS Submitted)
–Flare activity and photospheric analysis of Proxima Centauri (A&A 10-2017)
–A super-Earth on the inner edge of the habitable zone of GJ 625 (Ewass 2017 / JURA 2017)
–HARPS-N M-DWARF RV PROGRAM: A Super Earth orbiting a Nearby M-Dwarf (Pathways 2015)